I. Field of the Invention
The present invention relates generally to a filtering device and, more particularly, to such a device adapted for connection to the suction line of a hydraulic system.
II. Description of the Prior Art
Hydraulic fluid systems conventionally include a reservoir of hydraulic fluid, a suction line for fluidly connecting the reservoir to a hydraulic pump and a fluid return line from the hydraulic system and to the reservoir. The hydraulic fluid within the hydraulic system becomes contaminated during use and these contaminants must be filtered or removed from the hydraulic fluid in order to prevent damage to the hydraulic pump and other components of the hydraulic system. There have been a number of previously known fluid filtering devices which are fluidly connected to either the suction line from the reservoir or the return line to the reservoir.
In particular there have been a number of previously known suction line filters which include a tubular cylindrical housing having one end positioned within the fluid reservoir and into which a filter assembly is slidably received. The filter assembly typically includes an extension to coaxially secure it to a tubular filter element so that upon insertion of the filter assembly into the housing, the filter element is spaced radially inwardly from the interior walls of the housing and fluidly communicates between the reservoir and the hydraulic pump suction line.
One disadvantage of these previously known fluid filtering devices is that the extension assemblies for inserting the fluid filtering element into the housing are complicated and expensive in construction and yet not wholly satisfactory in operation. These extension assemblies conventionally include a seal arrangement comprising both a seal element and a seal carrier which sealingly engages the housing upon the insertion of the filter assembly. Due to frequent extraction and reinsertion of the filter assembly, and hence, the extension assembly, into the housing in order to replace or clean the filter element, the seal arrangement becomes rapidly worn and requires relatively frequent replacement due to the lengthy sliding engagement between the seal and the housing. Moreover, damage to the extension assembly from misuse or mishandling while extracted from the housing oftentimes requires expensive replacement of the entire extension assembly.
A still further disadvantage of the extension assembly employed with these previously known filtering devices is that a cover is conventionally secured across the upper axial end of the extension tube which abuts against the top of the main housing when the filter assembly is inserted therein. Bolt holes in the cover register with threaded bores in the main housing which receive bolts therethrough for securing the cover onto the main housing. However, upon insertion of the filter assembly into the main housing, the holes in the cover and housing typically do not register with each other so that the filter assembly must be rotated in order to bring these holes into alignment.
Rotation of the filter assembly after insertion into the housing, however, is difficult to accomplish due not only to the friction between the fluid seals and the main housing, but also since the fluid flow through the filter element hinders the rotation of the filter assembly. Moreover, since in many cases the extension assembly is screwed onto the filter element, rotation of the extension assembly in order to bring the mounting holes in alignment with each other oftentimes occurs without the desired rotation of the filter element, thus, loosening the connection between the extension assembly and the filter element which can cause undesireable fluid leakage.
A still further disadvantage of these previously known filter devices is that the filter element can be either inadvertantly or intentionally omitted from the extension assembly without detection since the cover closes the top of the main housing. When this occurs, unfiltered hydraulic fluid continuously enters and damages the hydraulic system.
A still further disadvantage of these prior devices is that the fluid inlet was typically positioned adjacent the bottom of the tank. As a result, scale and other debris from the bottom of the tank rapidly and uneconomically clogged the filter element. Many of these prior devices also filtered the fluid from the inside-out which creates undesirable fluid vortexes with entrained air in the fluid. Such entrained air can damage and/or cause cavitation in hydraulic machinery.
Many of these prior devices also included pressure indicating means secured to the filter extension assemblies for indicating the degree of clogging of the filter element. This, however, disadvantageously subjected the pressure indicating means not only to damage and abuse from repeated extraction and insertion of the extension assembly but also subjected the pressure indicator means to all length adjustments of the extension assembly.